1. Technical Field
This invention relates to a process for the production of ethylene homopolymers or copolymers of improved moldability characteristics with the use of a composite catalyst of specified compositions.
2. Prior Art
It is known that ethylene can be homo- or co-polymerized in the presence of Phillips type catalysts having chromium oxide supported on silica or the like. In general, this type of catalyst is subject to activation only under elevated temperature and pressure conditions and also susceptible to malfunction even on contact with a limited amount of impurities which will be present in ethylene monomers, .alpha.-olefin comonomers or solvents used. The Phillips catalyst has a further drawback in that it involves prolonged induction period and hence reduced production rate.
To cope with the above problems, a certain process of polymerization has been proposed in which a chromium oxide catalyst supported is employed in combination with a small amount of a reaction product of an organoaluminum compound with water as disclosed in Japanese Patent Publication No. 49-7341. Given a minimum induction period, however, this process is required to be effected in the presence of a chromium oxide catalyst calcined at high temperature and at a polymerization temperature not lower than 100.degree. C. so as to produce polyethylenes of great melt indices. To regulate the molecular weight of a polymer to be formed, the last-mentioned process is necessarily dependent upon the temperature of reaction rather than the feed of hydrogen. This mode of molecular weight control is difficult to accomplish with reliability. Such prior process is not wholly satisfactory in respect of the efficiency of operation.
A keen demand has been voiced for polyethylenes of superior melting and molding properties particularly in an industrial sector in which bottles of small dimensions are blow-molded for instance for daily use detergents.